Wrapping paper for photographic material



United States Patent 3,514,290 WRAPPING PAPER FOR PHOTOGRAPHIC MATERIAL Albert Emiel van Hoof, Berchem-Antwerp, Belgium, assignor t-o Gevaert-Agfa N.V., Mortsel, Belgium, a Belgian company No Drawing. Filed Apr. 29, 1966, Ser. No. 546,218 Claims priority, application Great Britain, Apr. 30, 1965, 18,334/ 65 Int. Cl. G03c 1/72 US. C]. 96-78 4 Claims ABSTRACT OF THE DISCLOSURE An opaque backing paper for photographic film composed of a single sheet of very thin flexible black paper, preferably kraft paper, which is itself pervious to light, the surface of the sheet facing the film being uncoated with the other surface carrying a layer of actinic-lightabsorbing pigment in a polymer latex binder and an exterior layer of a transparent protective coating, the overall film being opaque to light and of a thickness not exceeding 0.1 mm. For panchromatic film, the pigment is preferably carbon black and printing ink is applied between the pigment layer and protective coating for giving visible markings. For X-ray film, the pigment is preferably a yellow, orange or red organic pigment and the protective coating is waterproof.

The present invention relates to wrapping paper of a novel and very simple composition for photographic material.

According to the present invention there is provided a light-protective, photographically inert, thin and flexible wrapping paper for photographic material which wrapping paper is of a very simple composition and nevertheless is sufliciently opaque to prevent actinic visible light rays from passing therethrough.

The opaque wrapping paper according to the present invention consists of a single sheet of flexible black paper such black kraft paper having on one side thereof a coating containing in a latex as binder a pigment that absorbs actinic visible light to such an extent that the composite of black base paper and pigment coating is sufficiently opaque to prevent actinic light rays from passing therethrough and having a transparent protective coating over said pigment coating.

As a result of the simple composition of the wrapping paper according to the present invention it is possible to obtain wrapping paper having a thickness that does not exceed 0.1 mm. Therefore the wrapping paper according to the invention is particularly suitable for use as backing paper for photographic roll film and as packing paper for X-ray film in roll form, which packing paper can be applied according to the method and apparatus described and claimed in our co-pending British patent application 13,718/ 65. Of course, wrapping paper according to the present invention can be used for packing of all kinds of other photographic material too.

The black paper applied as base for the above wrapping paper is so thin and shows a lot of pinholes so that when taken alone it transmits light rays to cause film exposure. The pigmented latex coating renders the whole sufiiciently opaque to actinic light rays without adversely affecting the flexibility of the black base paper.

While black kraft paper having a weight comprised between about 65 and about 100 g./sq./ m. is particularly suitable for being employed as the base of the wrapping paper according to the invention any other paper that can be supercalendered to a thinness such that the paper itself plus the coatings thereon preferably does not exceed a thickness of 0.1 mm., could be used provided it has good strength and the paper plus the coatings thereon is sufficiently opaque to prevent light rays from passing therethrough.

In general, a paper suitable for being employed in the invention should preferably have an average tensile strength of at least 7 kg, measured longitudinally on a strip having a width of 15 mm., and a thickness preferably comprised between about 0.065 mm. and about 0.09 mm.

The pigment coating is preferably applied from a dispersion of finely divided pigment or mixture of pigments in a latex as binder. Any photographically inert organic as well as inorganic pigment that absorbs actinic visible light may be used. In fact, the choice of pigments for this invention is limited only by the requirement that, when coated on the particular paper used, they must give to the whole the required opacity, which depends on the kind and sensitivity of the photographic material in question.

For instance, in the case the wrapping paper is intended for use as backing paper for common roll film, the pigment used should in general absorb light of all regions of the visible spectrum since current roll films are panchromatic; thus, black pigments such as carbon black, oxides of heavy metals etc. are preferably used. In the case of X-ray film, however, red, yellow or orange pigments or mixtures thereof are preferably used; pigments of heavy metal salts should not be used in this case since on exposure to X-rays the said metal salts would be outlined on the film material.

Suitable pigments can for instance be selected from the various classes of readily dispersable pastes and pigments which usually contain a wetting agent as an adjuvant, which are marketed by Ciba A.G., Basel, Switzerland, Imperial Chemical Industries, Ltd., London SW. 1, England, Badische Anilin- & Soda-Fabrik A.G., Ludwigshafen (Rhine), Germany, Badische Anilin- & Soda-Fabrik, Ludwigshafen (Rhine), Germany and Kemisk Vaerk Koege A/S Copenhagen, Denmark. More specific examples of suitable pigments are Microsol Schwarz 2B paste (trade name for an aqueous carbon black dispersion), Monolite 30% by weight of solids), Aquadisperse 02/90 (trade name for an aqueosu carbon black dispersion), Monolite Fast Yellow CVS, a registered trademark for a pigment paste of the azo dye having the color index No. 11,765, Monolite Fast Red FLS, a registered trademark for a pigment paste of the azo dye having color index No. 12,460, Lithol'Rubine 4G, a registered tradmark for an azo dye having color index number 15,865, Paleogengelb RT Pigmosol, a registered trademark for a powdered form of yellow anthraquinone pigment, etc.

Any film-forming latex that has no detrimental affect on the photographic emulsion layer of the film and that is not tacky after drying is suitable for being employed as binder. Examples of suitable binders are for instance polyvinyl acetate, polystyrene, copolymers of styrene, copolymers of vinyl chloride, copolymers of vinylidene chloride, copolymers of alkylacrylates etc. Particularly suitable examples are copolymers of styrene and butadiene such as Butakon SL 103 (trade name for an aqueous colloidal dispersion containing 46.4% of solids marketed by Imperial Chemical Industries Ltd., London SW. 1, England), Dow Latex (trade name for a series of latexes of styrene-butadiene copolymers comprising from 60 to mole percent of styrene and from 46 to 48% by weight of solids marketed by the Dow Chemical Company, Midland, Mich, U.S.A.) such as Dow Latex 512R, Dow Latex 630 and Dow Latex 636, copolymers of vinyl chloride and butylacrylate such as Acronal 350D (trade name of Badische Anilin- & Soda-Fabrik, Ludwigshafen (Rhine), Germany) and copolymers of vinylidene chloride such 3 as the Saran Latexes F -122A and F 122-A (trade names of the Dow Chemical Company, Midland, Mich., U.S.A. for dispersions of vinylidene chloride-acrylonitrile copolymers in water comprising about 52% by weight of solids and 15% respectively 20% by weight of dib utyl phthalate as plasticizer).

The finely divided dispersions of pigment in a latex as binder may be coated on the black paper according to any suitable coating process, preferably by means of a brush spreader, an air-knife or doctor coater or by means of a rotogravure process wherein an intaglio roll provided with an etched screen is rotatably mounted in a pan containing the coating composition. A plurality of coatings of the same pigment or mixture of pigments may be spread onto the paper base by alternate coating and drying steps.

It is evident that filling agents and/or matting agents such as titanium white, which has a very good hiding power, as well as all kinds of other ingredients may be added to the pigment coating before applying them to the black paper base.

The pigment coating adheres very well to the black base paper and does not penetrate into said base paper so that the latter retains its good flexibility.

The pigment coating composition is applied in such a way that a satisfactory opacity is obtained, say preferably at a rate of about 10 to about 50 g. of dry substance per sq. m. of black paper.

After having coated the pigment layer, said layer may be given a smooth surface or glazing by calendering so that when printing on this surface sharp indicia are obtained, which do not become blurred. Indeed, the wrapping paper of this invention may bear printing matter, such as advertising matter and indicia indicating the kind of film; in the case the paper is intended for use as backing paper for roll film, numbers for indicating the exposed areas, warning marks, indica indicating the film speed etc. are provided on the paper.

For maximum visibility of the indicator markings through the camera windows, in the case of roll film, it is advisable to have the greatest possible contrast between the pigment coating and the printing thereon. Indicia in light colours such as shades of red, green, blue and yellow on a dark background or vice versa, indicia in dark colours on a light background, are most desirable from the point of view of appearance. The term colour used herein in relation to the overpointing which defines the printed matter (either negatively or positively), includes white and black.

The required indicia are printed on the pigment coating by means of rotating printing processes, preferably by rotogravure processes, by which processes it is possible to apply a sufliciently covering print in a continuous way. In these processes conventional printing inks with one of the above colours may be used. Suitable ink compositions for printing indicia by a rotogravure process on the pigment coating are alcoholic solutions of suitable colouring matter.

According to a special embodiment for printing the pigment coating, particularly in the case of photographic roll film, the indicator markings may be defined negatively i.e. by unprinted areas. In this case the pigment-latex coating is covered with the printing ink all over its surface except for the required indicia, which will appear as dark arates on a lighter coloured surface.

In order to protect the light-sensitive emulsion of a photographic material from the printing ink employed, more particularly in the case of roll film since the ink would adversely affect said emulsion when the film and backing paper are interwound in close contact on a spool, and/or in order to render the wrapping paper more or less water-tight, particularly in the case of X-ray film, the pigment coating is overcoated with a transparent photographically innocuous protective coating.

This coating can be a thin layer of a copolymer applied from an organic solution or from an aqueous dispersion (a so-called latex). Examples of polymers which are normally applied in dissolved state are cellulose derivatives e.g. cellulose nitrate, cellulose acetate, cellulose acetobutyrate and ethyl cellulose, chlorinated rubber, polyvinyl acetate, polystyrene, copolymers of vinyl chloride, copolymers of vinyl acetate, copolymers of vinylidene chloride, copolymers of alkyl acrylates, etc.

A coating of cellulose diacetate has proved to be par ticularly suitable to protect a photographic roll film, which is backed by a wrapping paper according to the present invention, against the printing on said wrapping paper, particularly because a cellulose diacetate coating, apart from giving a good protection against the ink, has very good antistatic properties and does not give rise to static discharges when being wound. Specific examples of polymers that are particularly suitable for providing a water-tight protective coating are copolymers of vinylidene chloride and acrylonitrile such as e.g. Saran Latex F 122-A 20 (trade name), copolymers of vinylidene chloride and methyl methacrylate such as Ixan WA 45 (trade name of Solvic S.A., Brussels, Belgium for a 55% anionic emulsion), Viclan vinylidene copolymer latexes (trade name of Imperial Chemical Industries, Plastics Division, Welwyn Garden City, Herts., England) such as Viclan VL 611 (trade name for an anionic dispersion containing 55% of solids), further Lutofan 1250 D (trade name of Badische Anilin- & Soda-Fabrik A.G., Ludwigshafen (Rhine), Germany, for a 40% aqueous plastic dispersion based on a copolymer of vinyl chloride which comprises 33% of the softening agent Palatinol C, trade name of the same firm for a dibutyl phthalate), Diofan 300 D (trade name for a 50% aqueous plastic dispersion based on a copolymer of vinylidene chloride, free from softening agents, marketed by Badische Anilin- & Soda- Fabrik A.G., Ludwigshafen (Rhine), Germany), and Plextol 350n (trade name for a 50% aqueous non-ionic dispersion of a plastic based on a copolymer of an alkyl methacrylate marketed by Rohm & Haas, Philadelphia, Pa., U.S.A.).

The latexes mentioned above for the protective coating may also be used as binder for the pigment coating so that one and the same latex can be used for both the pigment and the protective coating.

The protective overcoat is applied from a solution in a suitable solvent or mixture of solvents or from an aqueous dispersion and the coating may occur according to any suitable coating process, preferably by reverse roll coating (meniscus coating) in such a way that preferably from about 3 to about 20 g. of dry substance are present per sq. m.

The wrapping paper of the present invention has many advantageous features. For instance, the wrapping paper according to the present invention has a very simple composition and requires the least amount of coating materials. It was unexpected that only one pigment coating at only one side of a kind of paper as described could give the required opacity to make the paper suitable for use as wrapping paper for photographic material.

The Wrapping paper of the present invention having an overall thickness of at most 0.1 mm. offers the advantage, as compared with current duplex papers, which are rather thick, of adding additional exposures to photo graphic roll films, at least when using the spools that are in current use now. Since the wrapping paper of the present invention is much more flexible as compared with duplex backing papers less clock-springing of fresh film is found when the sealing label of the roll film is broken. In addition, as the wrapping paper is made Water-tight e.g. when used as packing paper for X-ray film, the photographic material can be used in the open under rainy conditions. Finally, the printing of the pigmented layer can be achieved more uniformly and the covering is much better than in those cases where the black paper itself is printed on.

The following examples illustrate more detailedly the composition of the wrapping paper according to the present invention, however, without limiting said composition thereto.

EXAMPLE 1 To a black kraft paper of 75 g./sq. m. the following composition was applied by means of a brush spreader:

Microsol Schwarz 2B paste (trade name) 210 Acronal 350 D (trade name) 275 by weight aqueous solution of Collacral P (trade name for a thickening agent on the basis of the ammonium salt of polyacrylic acid) 75 Water 440 This composition was applied in such a way that g. of dry substance were present per sq. m. of kraft paper. The kraft paper provided with the carbon black coating was glazed by supercalendering.

The required indicia were printed on the black pigmented layer obtained, by means of a yellow printing ink comprising lead chromate as pigment. The printed layer was then overcoated with a layer from a solution of cellulose diacetate in acetone and ethylene glycol monomethyl ether in such a way that from 3 to 6 g. of dry substance were present per sq. m. The cellulose ester solution was prepared by dissolving 10 kg. of low viscosity cellulose diacetate in acetone whereupon the volume was brought to 150 litres and then 15 litres of ethylene glycol monomethyl ether were added.

EXAMPLE 2.

This example is analogous to Example 1 with the difference, however, that Dow Latex 512 R (trade name) was used as latex instead of Acronal 350 D (trade name).

EXAMPLE 3 By intensively stirring, the following ingredients were thoroughly mixed:

Water 330 Titanium white 225 Casein 28 Ammonium hydroxide (d=0.91) 7 Thereupon the following products were portion-wise added.

G. Monolite Fast Yellow CVS paste (trade name) 270 Monolite Fast Red LFS (trade name) 50 Butakon SL 103 (trade name) 90 In this way mixture I was obtained.

Mixture H was prepared from the following ingredients.

G. Viclan VL 611 (trade name) 660 Ammonium hydroxide (d=0.91) 30 Dibutyl phthalate emulsion 310 This emulsion was prepared by mixing, while intensively stirring, 155 g. of Water, 153 g. of dibutyl phthalate and 2 g. of Ultravon W (trade name for the sodium salt of heptadecylbenzidazole-disulphonic acid marketed by Ciba AG, Basel, Switzerland).

By means of. an air-knife coater mixture I was applied to a black kraft paper of g./sq. m. pro rata of 20-25 g. of dry substance per sq. m. The paper base provided with the pigmented coating was then overcoated with mixture II pro rata of 1015 g. of dry substance per sq. m.

EXAMPLE 4 By means of an air-knife coater a black kraft paper of 85 g./sq. m. was coated pro rata of 20-25 g. of dry substance per sq. m. with a mixture having the same composition as mixture I of Example 3 with the only difference that the amount of Butakon SL 103 (trade name) was replaced by a same amount of Dow Latex 636 (trade name).

The paper base provided with the pigmented coating was then overcoated with Ixan WA 45 (trade name) pro rata of 10-l5 g. of dry substance per sq. m.

I claim:

1. Roll film comprising a strip of light-sensitive photographic film and a strip of opaque backing paper for said film, said backing paper consisting essentially of a single sheet of supercalendered flexible paper which is black in coloration throughout its thickness and of such thickness alone as to be previous to light, said paper having the side thereof adjacent said film uncoated and on the exterior side thereof layers comprising a coating of carbon black in a polymer latex binder wherein said polymer is selected from the group consisting of styrene-butadiene copolyrners, vinyl chloridebutyl acrylate copolymers, and vinylidene chloride copolymers, ink printing on said coating, and an exterior transparent protective coating selected from the group consisting of cellulose diacetate and ethyl cellulose, the complete backing paper being opaque to actinic light and having an over-all thickness not exceeding 0.1 mm.

2. Wrapping paper according to claim 1, wherein the sheet of black paper is a sheet of black kraft paper.

3. Wrapping paper according to claim 1, wherein the black paper is a paper of a weight comprised between about 65 and about g./sq. m.

4. Wrapping paper according to claim 1, wherein the black paper is a paper of a thickness comprised between about 0.065 and 0.09 mm.

References Cited UNITED STATES PATENTS 2,646,366 7/1953 Baxter 9678 XR 2,751,309 6/1956 Baxter 96-78 3,021,214 2/1962 Murphy 96-85 DAVID KLEIN, Primary Examiner US. Cl. X.R. l17155 

